<template>
  <div class="todo-footer">
        <label>
          <input type="checkbox" v-model="isAllCheck"/>
        </label>
        <span>
          <span>已完成{{completeSize}}</span> / 全部{{todos.length}}
        </span>
        <button class="btn btn-danger" v-show="completeSize" @click="deleteCompleteTodos">清除已完成任务</button>
      </div>
</template>
<script>
export default {
  // 先想好属性，然后去App.vue里改TodoFooter组件标签
  props:{
    todos: Array,//有了todos就能知道全选按钮和所有todo的个数。
    deleteCompleteTodos:Function,//删除所有的按钮功能
    selectAllTodos:Function,//全选功能
  },
  //统计完成的个数
  computed: {
    completeSize(){
      return this.todos.reduce((preTotal, todo) => preTotal + (todo.complete?1:0),0);
    },
    isAllCheck:{
      get(){//返回完成个数是否等于todos的长度，true、false
        return this.completeSize===this.todos.length && this.todos.length>0;
      },
      set(value){//value是当前checkbox最新的值
      this.selectAllTodos(value);
      }
    }

  }

}
</script>

<style>
/*footer*/
.todo-footer {
  height: 40px;
  line-height: 40px;
  padding-left: 6px;
  margin-top: 5px;
}

.todo-footer label {
  display: inline-block;
  margin-right: 20px;
  cursor: pointer;
}

.todo-footer label input {
  position: relative;
  top: -1px;
  vertical-align: middle;
  margin-right: 5px;
}

.todo-footer button {
  float: right;
  margin-top: 5px;
}

</style>